1. Field of the Invention
The invention is concerned with the field of injection molding, and more particularly with the field of injection molding as applied to the formation of impedance measuring modules. More particularly yet, the invention is concerned with the formation via injection molding of an impedance measuring module with a metal grid completely imbedded in plastic with the exception of the leads thereof and of a pair of pluralities of electrodes, one pair of electrode within each chamber or cell of the impedance measuring module.
2. Prior Art
The use of electrode containing measuring cells to determine whether or not microorganisms are present in samples injected in said cells through measurements of changes in impedance therein is known as described for example in U.S. Pat. No. 3,743,581, commonly assigned herewith. The use of impedance measuring modules which have a plurality of cells upraised therefrom is also known as taught for example in U.S. Pat. No. 3,890,201, also commonly assigned herewith. In the latter patent, the modules are formed from circuit board-like boards having the conductors upraised therefrom and plastic modules or the like are glued or otherwise fastened in place atop the conductors on said boards whereby a pair of electrodes are exposed in the interior of the chambers formed on the boards. Such modules are not readily adaptable to rapid mass production methods and, further, since the metal conductors atop such boards are exposed they may be fairly easily damaged through rough handling and the like.
Accordingly, the present invention is concerned with the formation of impedance measuring modules wherein a metal conducting grid within the module is substantially completely imbedded in plastic to protect it from harm. The production of such modules has, however, created certain problems unique to the design of the modules. Most particularly, it has been necessary to design an injection mold wherein a metal grid can be properly placed therein and yet wherein the electrodes which extend from the grid can be protected from coating by the plastic injected into the injection mold so that the impedance between these electrodes and, accordingly, any changes in the impedance between these electrodes can be accurately measured.
Accordingly, having realized the problems inherent in adapting injection molding techniques to formulating impedance measuring modules, the present invention provides a particular mold design and a particular injection molding process which allows for the mass production of impedance measuring modules with the electrodes therein free of plastic and properly spaced from one another yet with the grids thereof otherwise generally imbedded in plastic. The mold and process of the present invention thus provide fast and inexpensive operation available with injection molding along with substantially complete imbedding of the conducting member of the module so as to protect it from bending, scratching and the like.